diff --git a/backup.sh b/backup.sh
index ed31ba6..755a6b6 100644
--- a/backup.sh
+++ b/backup.sh
@@ -18,6 +18,8 @@ if [ $UID -ne 0 ] ; then
   exit 1
 fi
 
+backupdir=/var/backups/$(date -I)
+
 while getopts hl OPTION ; do
    case $OPTION in
    (l) listBackups ${backupdir}/.. ; ;;
@@ -26,9 +28,8 @@ while getopts hl OPTION ; do
    esac
 done
 
-shift $((OPTIND -1))
+shift $(( OPTIND - 1))
 
-backupdir=/var/backups/$(date -I)
 mkdir -p $backupdir || myerror 2 "impossible de créer $backupdir"
 
 for dir in "$@" ; do